1. Field of the Invention
The present invention relates to a lead frame adapted to be used for a semiconductor device and a method for manufacturing the same.
2. Description of the Related Art
In general, lead frames for use in semiconductor devices are manufactured by punching or etching metallic materials.
However, in the case of punching or etching, the minimum processing width is approximately the same as the material thickness so that the processing range is limited, and there is a limit to forming a fine pattern from a material of a predetermined thickness.
On the other hand, as well known, there is provided a method for manufacturing lead frames by means of electro-forming (disclosed in Japanese Examined Patent Publication (Kokoku) No. 48-39867).
This known electro-forming process is shown in FIGS. 7(a), (b), (c), (d) and (e), and will be described below: A resist 11 is coated or adhered on a matrix 10 made of conductive material such as stainless steel, as shown in FIG. 7(a); pattern printing is conducted, as shown in FIG. 7(b); developing is conducted so as to form a resist pattern 12, as shown in FIG. 7(c); when this resist pattern is used as a mask, an electro-deposition pattern 13 is formed on the matrix 10 by means of plating, as shown in FIG. 7(d); the resist pattern 12 is removed; and further the electro-deposition pattern 13 is separated from the matrix 10, as shown in FIG. 7(e).
Next, the electro-deposition pattern 13 is subjected to necessary plating. In this way, a lead frame is manufactured.
In some cases, after the resist pattern 12 has been removed from the matrix 10, a surface of the electro-deposition pattern 13 is ground so that the thickness of the electro-deposition pattern 13 can be made uniform.
According to this electro-forming process, a lead frame having a very fine pattern, the section of which is rectangular, can be accurately manufactured.
In the above manufacturing process of lead frames, the following problems may be encountered: When the electro-deposition pattern 13 is separated from the matrix 10 in the electro-forming process, the electro-deposition pattern 13 may be deformed. Also, the electro-deposition pattern 13 may be deformed in the processes conducted after electro-forming, for example, in the process of plating. Further, in the case where the electro-deposition pattern 13 is ground, the electro-deposition pattern 13 tends to be deformed. Such a deformation of the electro-deposition pattern 13 may become substantial when the pattern is fine.
Also, if the inner lead pattern becomes finer, the resist pattern 12 for the mask must become finer and, therefore, the electro-deposition pattern 13 must be developed in narrow recesses of the resist pattern 12. When electro-forming is conducted, hydrogen is generated due to a negative pole reaction. If the resist pattern 12 is narrow as mentioned above, the hydrogen particles in small bubbles will be attached to the inner walls of the resist pattern 12 because the plating liquid does not flow smoothly. Therefore, a good plated film is not formed, since small pits or holes are formed in the electro-deposition pattern 13.